Junior men's skater Emmanuel Savary, 12, of Newark, demonstrates a "death drop" jump at Gold Arena at the University of Delaware. / The News Journal/FRED COMEGYS

THE SKATE

Unlike hockey skates, figure skates have a set of large jagged teeth called toe picks on the front of the blade. These are used for jumping and footwork.

The blade of a figure skate is not flat but slightly curved, forming an arc of a circle with a radius of 180 to 220 cm. This curvature is referred to as the rocker of the blade. The sweet spot of the blade is below the ball of the foot and is the part of the blade where spins are executed called the spin rocker.

Blades are also hollow-ground. The groove on the bottom of the blade creates two distinct edges, inside and outside. The inside edge of the blade is on the side closest to the skater. The outside edge is on the side of the blade farthest from the skater. Figure skaters always skate on one edge of the blade, never on both sides at the same time, which is referred to as a flat, as they derive power from the efficient use of the edges to generate speed.

THE FIRST SKATES

The oldest pair of skates known date back to about 3000 B.C., found in a lake in Switzerland. The skates were made from the leg bone of a horse, holes were bored at each end of the bone and leather straps were used to tie the skates to the feet.

FRICTION

The difference between dancing on a floor and skating on ice is the lack of friction in skating. Skates allow a person to move very quickly across the ice because there is very little friction between the blade of the skate and the ice. This lack of friction is partially due to the interaction of steel with ice and partially due to the very small surface area making contact with the ice. Friction from the metal rubbing against the ice causes it to melt. This is also the reason when you are ice skating a track is formed. The track is because of the gap that has been made when the ice melts. The water formed may help lubricate and reduce friction along the blade.

Beyond the grace, style and athleticism of routines that have made international celebrities of such skaters as Michelle Kwan, Kristi Yamaguchi and Scott Hamilton, there are simple scientific concepts at work as they glide across the ice.

Whether you watch figure skaters competing at the Olympics or people having fun at your neighborhood rink, they all are making use of basic scientific principles such as friction, momentum and the law of equal opposite reaction.

The difference between walking on a floor and skating on ice is the lack of friction -- the force that occurs when two objects slide against each other dissipating their energy of motion. The rougher the surfaces, the greater the force of friction they will exert. The smooth surface of the ice allows the skater to glide across without friction stopping her as soon as she has begun.

The skate plays a role as well. The skating boot is equipped with a thin, slightly curved piece of tempered steel attached vertically to the exterior of the sole. This blade ensures that a minimal area comes into contact with the ice, reducing resistance in the form of friction.

The pressure of the blade on the surface of the ice also causes the ice to melt, producing a thin layer of water between the solid ice and the edge of the skater's blade.

"This layer of water gives you very little friction," said Dr. Harry Shipman, professor of physics and astronomy at the University of Delaware. "But if your balance isn't certain and your skates are wobbly, you're going to put more pressure on more layers of water, causing you to slow down. You have to manage the friction as much as you can."

But friction does play an important role in figure skating. Without it, skating would not be possible. Remember Newton's first law of motion? An object in motion tends to stay in motion unless acted on by a force. It is the force of friction between the skate and the ice that allows the skater to come to a stop.

Figure skaters often embellish their routines by spinning fast in one spot. The skater accomplishes this without falling down because of a concept called angular momentum that helps to stabilize a moving body rotating around a fixed object. The momentum of spinning objects like tops or figure skaters is a combination of the size of the person or mass, the speed and the radius of the object, or in the case of figure skating, the distance from the center of the person to the outermost part of his body.

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A fundamental law of physics states that momentum -- the amount of force it would take to stop a moving object -- is always conserved. This law explains why as a skater pulls her arms close into her body, she spins more quickly. With arms outstretched, her mass is distributed over a greater space and she spins more slowly. When she pulls her arms inward, the distribution is reduced, so the speed picks up to counteract this difference and keep her momentum constant.

A basic tenet of physics holds that for every action there is an equal and opposite reaction, and it is this law that allows the skater to begin moving and to execute jumps. When a skater pushes down and against the ice, the ice generates an upward force that propels her into the air.

Balance also is crucial to figure skaters. It keeps them from falling when landing after a jump.

"If you don't have a good solid core, your upper body will be off from your lower body, making it very difficult to stay vertical in the air," said Christie Moxley, a figure skating coach at the University of Delaware. "That's one of the things that cause skaters to fall."

Of course, it is not the knowledge of the physics of figure skating that makes a great skater, but the practice -- four 40-minute sessions at UD's Gold Arena on a recent day for 13-year-old Kara Morris of Dover -- and the effort she invests. Still, knowing the mechanics of the sport can help.

"It's important for athletes to understand the physics of what they're doing," Moxley said. "The older the skater gets, the more you'll see them translating what they've learned at a more advanced level."

COMMON SPINS AND JUMPS

JUMPS

There are two types of jumps in figure skating: "toe" jumps and "edge" jumps.

In a toe jump, the skater uses the jagged edge of the skate's toe pick of the leading foot to vault into the air off the edge of the other foot. In the edge jump, the skater takes off directly from the edge of the foot that is behind. This technique adds less height to the jump, but allows for smoother movement. Some of the most common jumps are:

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* Toe loop: Originated by Bruce Mapes in the 1920s, this jump requires that the skater be skating backward on an outside edge. Then, using the toe pick of the other foot, he vaults himself into the air, completes half a revolution in the air, and then lands on the other foot.

* Salchow: This is an edge jump launched off the back inside edge of one foot and landed on the back outside edge of the opposite foot. It takes its name from its originator, Ulrich Salchow, who won 10 World Championship titles from 1901 to 1911.

* Flip: A toe-pick-assisted jump launched from the back inside edge of one foot and landed on the back outside edge of the opposite foot.

* Lutz: Named after its originator, Austrian Alois Lutz, this is a toe-pick-assisted jump launched from a back outside edge and landed on the back outside edge of the opposite foot. The skater glides backward on a wide curve, taps his toe pick into the ice and rotates in the opposite direction of the curve.

* Axel: Named after its Norwegian originator Axel Paulsen, it is the only jump that takes off from a forward position. Skaters launch into the air from their forward outside edge and land on the back outside edge of the opposite foot. The toughest part is that there needs to be one and a half revolutions in the air.

SPINS

There are three basic positions for figure skating spins: upright, sit and camel.

* Scratch: One of the most basic of all spins, the scratch spin consists of the skater standing up straight over the left leg while spinning on an inside edge. The right leg is extended in front of the body with the thigh raised high, and the arms are up and out to the side. Bringing in the free leg and the arms accelerates the spin.

* Layback: Generally performed by women, this upright spin requires the skater to arrange her arms in a circle in front of her body, arch her back and look toward the ceiling while spinning. The spin was invented by Cecilia Colledge of Great Britain.

* Biellmann: This spin, named for Swiss skater Denise Biellmann, who popularized the move, requires the skater to grasp her foot and pull it above her head.

* Camel: This is a spin on one leg with the non-skating or free leg extended parallel to the ice and the upper body pitched forward, arms extended. When the camel spin was first invented, many skaters would make a hump with their rear ends. Their head and free leg would fall below the hips. That mistake caused the spin to eventually be called the "Camel Spin."

* Doughnut: This is a variation of the camel spin in which the skater grabs his skate from behind and pulls the head toward the free leg's foot so that the head, torso and free leg form a doughnut shape parallel to the ice.